In the conventional art, so-called compact disks (hereinafter referred to as CDs) where pieces of music information are recorded as digital signals through mechanical pits, are widely used. Information recorded on CDs is reproduced by means of a disk reproducing device used only for reproducing.
In a CD, a plurality of pieces of information are usually recorded in succession. During the reproduction, absolute addresses previously recorded on the disk and absolute addresses indicating the recording start position of each piece of information and being recorded in a TOC (Table Of Contents) area provided in the inner periphery or other location of the disk, are compared, and the desired pieces of information may be reproduced successively or selectively.
When recording pieces of music information on or using rewritable disks that have been developed recently such as magneto-optical disks, Direct Read after Write type disks in which information can be recorded only once, or other types of disks, a compatible disk recording/reproducing device using a common method of reproduction for such magneto-optical disks and conventional CDs needs to be provided. In this case, a so-called constant linear velocity (CLV) that is employed in reproducing devices for CDs may be adopted as control method for the disk rotation during the recording and reproduction.
Among the sampling frequencies used in recording mediums whereon digital information is recorded, for instance the sampling frequency used in Digital Audio Tapes (hereinafter referred to as DATs) equals 48 kHz, and the sampling frequency used in satellite broadcasting equals 32 kHz. That is, both DATs and satellite broadcastings have sampling frequencies different from the sampling frequency used in CDs which is equal to 44.1 kHz. However the information recorded on these digital recording mediums needs to be recorded as it is on the writable disks described earlier.
When recording pieces of digital information such as pieces of music information etc., produced by different sampling frequencies together on a single disk in their respective recording frequencies, to make the recording density of the information on the disk approximately uniform and independently of the sampling frequencies, the linear velocity on the disk has to be changed according to the sampling frequency of the information to be recorded so that information having a high sampling frequency is recorded and reproduced with a high linear velocity.
In this case, when reproducing pieces of information successively, the linear velocity needs to be changed at the boundary separating pieces of information each time the sampling frequency changes. This not only causes the burden on the motor to be increased and might shorten its life span, but also gives rise to problems such as an increase in the latency due to the change in the linear velocity.
In the conventional art, a method for forming the absolute addresses on a disk such as a writable disk, has been discussed where the absolute addresses are written by having guiding grooves snake on the disk such that the pitch of the undulation in a radial direction (wobbling) corresponds to the absolute addresses. When recording the absolute addresses using guiding grooves that snake in the manner described above, an absolute address is usually recorded after having passed through an FM (Frequency Modulation) process where the frequency of a carrier wave having a constant amplitude is modulated by an absolute address signal. Consequently, in order to reproduce an absolute address during the recording of information, the frequency-modulated signal needs to pass through an FM demodulation process that converts the frequency of the frequency-modulated signal into an amplitude.
However, during the recording or reproduction, when changing the rotational speed of the disk in accordance with the sampling frequency of the different pieces of information as described above, the cycles of the snaking guiding groove are modified due to the variation in the rotational speed of the disk. This causes an accurate demodulation of the absolute addresses to be infeasible.